Converters with electrical isolation are used for the galvanically decoupled transfer of electrical energy from an input side to an output side. Such converters are used in various applications for supplying current or voltage, such as, for example, in clocked switched mode power supplies. In the case of clocked converters, controllable switches, which can be configured in the form of power switches, are used and are operated in clocked fashion in order to transfer electrical energy to the output side. A galvanically decoupled energy transfer can be achieved by the use of a transformer or another transfer device. Such a galvanic isolation or electrical isolation is required for safety reasons in order to isolate an ELV (“extra-low voltage”) region from regions with a relatively high supply voltage, in particular mains voltage, by means of a so-called potential barrier or SELV barrier.
Converters which are configured as so-called resonant converters which have a resonant circuit can be used for operating light-emitting means. The resonant circuit can be a series or parallel resonant circuit. When configuring converters, the aim is to keep losses low. In the case of converters which are intended to be suitable for operation of dimmable light-emitting means, in particular of light-emitting diodes (LEDs) such as inorganic LEDs or organic LEDs (OLEDs), there is increasingly the demand for enabling dimmability over a wide range.
One possibility of regulating an output current or an output voltage on the ELV side of an operating device consists in detecting and processing a controlled variable on the ELV side. The regulation step can take place completely on the ELV side, wherein, for example, a switch on the ELV side is actuated depending on the controlled variable. Alternatively, the regulation step can also be implemented on the input side of the converter, which is operated at a higher supply voltage. However, until now this has required that the controlled variable detected on the secondary side is fed back to the input side via an insulator. The bypassing of the SELV barrier requires corresponding components which increase the installation space required and/or the costs of the operating device. US 2012/0033453 A1 describes an example of a resonant converter which comprises a half-bridge and an LLC circuit and in which an insulator is provided in order to feed back a variable measured on the output side to the input side. US 2012/0033453 A1 describes an example of a resonant converter in which switches in a low-voltage region of the converter are actuated depending on a controlled variable detected on the secondary side.
There is a need for apparatuses and methods which provide improvements in respect of the mentioned objects. In particular, there is a need for apparatuses and methods in which the complexity in terms of circuitry and/or the costs which are associated with the bypassing of the SELV barrier can be reduced or avoided. There is also a need for those apparatuses and methods which enable efficient energy transfer and dimmability over a wide range.